Recently, lighting units etc. formed with a light emitting diode (LED) have long lifetime and consume low power as a with existing incandescent lights or fluorescent lights, and demand thereof is significantly increasing due to the advantage of not releasing pollutants in the manufacturing process. In addition, LEDs are being applied to backlight devices of lighting apparatuses or LCD displays as well as display devices requiring light emitting, such that application areas thereof are widening. Particularly, LEDs have low heat and long life due to high energy efficiency while being driven with relatively low voltage, and as technologies capable of providing white light with high-brightness that was difficult to implement in the related art are developed, it is expected that most light source devices being currently used may be replaced with LEDs.
The LED is sold-state device converting electrical energy into light, and generally includes an active layer of semiconductor material interposed between two facing doped layers. When applying bias to both ends of two doped layers, and after holes and electrons are injected into the active layer, holes and electrons are recombined at the active layer to generate the light. Then, the light generated from the active layer is emitted in all directions, and is emitted outside a semiconductor chip through all exposed surfaces.
A typical structure of nitride semiconductor light emitting diode includes a buffer layer, an n-type nitride semiconductor layer, an active layer of a multi quantum well structure and a p-type nitride semiconductor layer, and the p-type nitride semiconductor layer and the active layer are partially removed by etching etc., such that some of the top of the n-type nitride semiconductor layer is exposed. An n-type electrode is formed on the exposed n-type nitride semiconductor, a transparent electrode layer forming ohmic contact is formed on the p-type nitride semiconductor layer and then, a p-type bonding electrode is formed.
In the light emitting diode formed by a method of manufacturing the light emitting diode in the related art, to form the n-type electrode on the n-type nitride semiconductor layer, since the active layer should be partially removed, there is a problem that light output is weakened due to the loss of the active layer.
Further, there are problems that efficiency of the reflective film is lowered due to the metal pad formed to be relatively large as compared with the chip size.
Therefore, requirements for light emitting devices are as follows. Firstly, the loss of the active layer due to mesa etching etc. forming an n-type electrode is not generated; secondly, when forming the n-type electrode, the loss of the active layer is minimized, thereby to control the size and position of a p-type electrode, such that the brightness may be improved; thirdly, a chip size has flexibility by forming one chip bound with a number of unit cells; and fourthly, although the light emitting diode is formed by binding a number of the unit cells, the light output is improved by filling a reflective layer or current diffusion layer between the unit cells.